1. Field of the Invention
The present invention is directed to a recirculation valve for recirculating fluid back to a centrifugal pump in order to prevent damage to the pump during intervals when there is minimum demand for the pumped fluid downstream of the valve. More particularly, the present invention is directed to a recirculation valve having a two angle control surface between the check valve disc and the valve casing in order to provide a more linear relation between the position of the check valve disc and the amount of flow. The valve also allows the snap-in of different size spiral rings onto the check valve disc to change the Cv of the valve and the use of similar rings to change the Cv of the recirculation flow. The second angle provides clearance for the snap-on ring while maintaining linear characteristics for the both high main flow applications (no ring) and low flow applications (with ring).
2. Description of the Prior Art
Centrifugal pumps are used in a variety of applications. It is often desirable to recirculate fluid back to a centrifugal pump during intervals of low demand by an outlet device to prevent the pump from overheating. Overheating is caused by the exchange of heat between the running pump and stationary fluid present within the pump. Pump overheating lowers the vapor pressure, resulting in fluid cavitation which can destroy the pump housing and impeller.
Recirculation valves are frequently used in centrifugal pumps to control overheating. One commonly used recirculation valve is a modulating flow control valve disclosed in U.S. Pat. No. 4,095,611. The valve disclosed in U.S. Pat. No. 4,095,611 has a circular disc-shaped check valve member interposed within a two-piece valve casing. During periods of normal downstream fluid demand, a pressure differential across the valve causes it to open and permit flow while simultaneously blocking a fluid recirculation passageway. Conversely, during intervals of minimal downstream fluid demand, the disc-shaped check valve member returns to a closed position, thereby opening the fluid recirculation passageway and permitting fluid to recirculate back to the pump.
Another recirculation valve, disclosed in U.S. Pat. No. 4,243,064, has a circular main valve disc and bypass valve disc axially displaced at both ends of a connecting valve stem. During periods of normal fluid flow, the connecting valve stem moves to an open position causing fluid to flow out both the main outlet and the bypass outlet. When fluid flow is minimal, the bypass valve disc is superimposed over an annular seat which causes fluid to be redirected from the main outlet to the bypass outlet and recirculated through the centrifugal pump.
A problem encountered with the use of such recirculation valves is that the relation between the movement of the check valve means and the amount of recirculation flow does not always follow a linear relationship. Such a linear relationship allows more precise control of the amount of recirculation.
It is an object of the present invention to provide a recirculation valve having a two angle control surface between the check valve disc and the valve casing in order to provide a linear relationship between the open position of the check valve disc and the flow of fluid being recirculated. The main advantage of a dual angle is to maintain good linearity with and without the ring. It is more economical to provide a single body design. The dual angle allows the use of an inexpensive ring to change the main flow capacity and maintain good linearity.
It is a further object of the present invention to provide a recirculation valve wherein the Cv can be readily changed through the installation of different size spiral rings on the check valve disc.
It is an additional object of the present invention to provide a recirculation valve mechanism capable of being preset to allow given recirculation flow rates by presetting the position of the cylindrical bushings within the valve.
Another object is to provide multiple bypass inlet paths to provide greater bypass flow capacity for the same size bypass valve stem. A further advantage of this construction is that the upper bypass inlet ports provide another flow path through the valve stem when the valve is open providing increased main flow capacity.
These and other objects of the present invention and the various features and details thereof are hereinafter set forth in the following detailed description of the invention.